Probability of finding a particle in the ground state

A particle is prepared in the state [tex]\psi (x) = \frac{1}{\sqrt{L}}[/tex] in a region [tex]0 < x < L[/tex] between two hard walls (particle in a box). Calculate the probability that the particle is found in the ground state when its energy is measured.

2. Relevant equations

This question is worth 10 marks, so I presume it's not as simple as squaring the wave function to find the probability. However I'm just not sure what else to do, a hint in the right direction would be greatly appreciated.

3. The attempt at a solution

[tex]\left| \psi (x) \right|^{2} = \frac{1}{L}[/tex]

That's all I can think of doing. I've checked the given wave function is normalised, which it is.